In vertebrates, the ectoderm is subdivided during gastrulation into four primary fates: epidermis and central nervous system (CNS) on the ventral and dorsal surfaces, respectively, and neural crest and sensory placodes located between these two domains. The goal of this project is to understand the mechanisms that determine how ectodermal cells choose between these pathways, and how the ensuing tissue patterning and differentiation are regulated. The experimental approach taken by this laboratory has been to use dependence upon cell-cell signaling as a criterion for identifying genes that may regulate the ectodermal developmental programs. Attention has been focused on four homeobox genes, Msx1, Dlx3, Dlx5 and Dlx6, and on the transcriptional activator AP-2alpha. We have found that the four homeobox genes are differentially regulated by a graded response to bone morphogenetic protein (BMP) signaling, resulting in different expression boundaries in vivo. We theorize that this can account for at least some of the major features of the spatial patterning of ectoderm during gastrulation. Msx1 appears to be involved in establishing the anterior boundary of the cement gland, a structure demarcating the most forward aspect of the neural plate, and in the induction of neural crest. Dlx3 seems to function in setting up the lateral boundary of neural crest. The roles of Dlx5 and Dlx6 may be related to establishing the boundary of the neural plate, and also in the formation of the sensory placodes. Neural crest induction in Xenopus requires two signals, a partially attenuated BMP signal and a Wnt/beta catenin signal. We have found that AP2alpha is responsible for conveying the BMP signal to the genome, and activation of a broad spectrum of neural crest-specific genes. AP2alpha is also imporant in the development of epidermis. We are using a hormone-inducible version of AP2alpha as a tool in conjunction with microarray analysis to identifiy target genes in both epidermis and neural crest. Several hundred such genes have now been identified, many of which have known functions such as transcription factors, signaling molecules, extracellular matrix-related enzymes and other structural or enzymatic functions. Many also have no known function, but are conserved in the mouse and human genomes and are thus likely to be important. We are now using antisense oligonucleotides and other strategies to study these functions, with the goal of learning how genes interact to control the formation and differentiation of epidermal and neural crest cells in the frog embryo. Since these tissues and genes are conserved throughout vertebrate phylogeny, our findings should have broad relevance to biomedical research and human health and development.